This invention relates to writing instruments with retractable tips and more particularly to such instruments in which relative rotation of portions of the body of the instrument effects retraction and projection of the writing tip.
Numerous writing instruments with retractable tips have been known. These have often employed complex internal mechanisms to effect projection and retraction of the tip of, for example, a ball-point cartridge, spring biased towards the retracted position. Internal cams have been employed to this end, and these have been activated and released by push buttons, located at the end of such instruments or beneath the pocket clip, or by rotation of a part of the body of the instrument.
In twist-activated instruments, relative rotation between halves of the instrument body causes projection and retraction of the writing tip. Internally housed cam members, turned by the relative rotation of the housing parts, have forced projection of the writing tip against the bias of the spring when the two body portions are rotated with respect to one another. In these instruments, the two body portions, ordinarily a barrel and a cap, do not move axially with respect to each other, but cause the relative rotation of the internal cam parts that effects axial movement of a cartridge by cam operation. These instruments have been unduly complex by virtue of their internal construction. In some of these, separate provision had to be made to prevent separation of the relatively rotatable body portions of the instrument.
Simplification of the actuating provisions of writing instruments with retractable points reduces costs significantly, not just by reducing the number of working parts and hence the cost of manufacture, but by simplifying assembly and in that way reducing manufacturing cost. Likewise, elimination of the need for separate provisions preventing disassembly of the instrument could further simplify production and assembly and lead to cost reduction.